Electrical musical instrument



Aug. 9, 1949.

J. M. r-mlvEFaTl ELECTRICAL MUSICAL INSTRUMENT 4 Sheets-Sheet l Filed March 20, 1942 www @www w @www J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT Aug. 9, 1949.

Filed March 20, 1942 4 Sheets-Sheet 2 J///m? 0 f2 l. mer

J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT Aug. 9, 1949.

4 Sheets-Sheet 5 Filed March 20, 1942 fnl/enfer Joh/2 JIJ. Hana/"2 Auge 99 1949, .1. M. HANERT 2,478,867

ELECTRICAL MUSICAL INSTRUMENT Filed March 20, 1942 4- SheeCS-Sheet 4 Huiuul um W mz es #ma was l/os Patented Aug. 9, 1949 ELECTRICAL MUSICAL INSTRUMENT John M. Hanert, Wilmette, Ill., assignor to Hammond Instrument Company, Chicago, Ill., a

corporation of Delaware Application March 20, 1942, Serial No. 435,499

37 Claims.

My invention relates generally to electrical musical instruments and more particularly to a solo instrument of this type.

It is an object of my invention to provide an improved solo type electrical musical instrument in which the intensity envelopes of the tones may be readily controlled.

A further object is to provide an instrument of the foregoing type in which the player, by the extent of depression of the playing keys, may control the intensity envelopes of the tones.

A further object is to provide an improved tone quality modulating eiect in the output of an electrical musical instrument, in the nature of a quality vibrato.

A further object is to provide a second touch tone intensity envelope controlling circuit in which the character of the envelopes of the tones may be preselected.

A further object is to provide an electrical musical instrument having pitch determining playing keys, and having a separate group of tone intensity envelope determining keys playable simultaneously with the pitch determining keys.

A further object is to provide an electrical musical instrument having an output system including a non-linear distortion circuit, the output of which comprises predominantly the odd harmonics of the fundamental frequency of the input signal.

A further object is to provide an electrical musical instrument having a plurality of interlocked octave interval oscillators tunable by the playing keys throughout the range of several octaves, and having output circuits which may be employed singly or in combinations to provide octave coupler effects.

A further object is to provide an output circuit for an electrical musical instrument having an electron discharge device provided with a control grid and a second grid, such as a screen grid, in

which the amplitude of the signal transmitted by the device is determined by a resistance-capacity network connected to the second grid in a manner such that the current drawn by said second grid may change its effective potential.

A further object is to provide an improved expression control for electrical musical instruments in which the natural frequency of a tone quality mesh is shifted as the volume is changed.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

Figures 1, la and 1b together constitute a wir- `ing diagram of the complete instrument less the power supply system;

Figure 2 is a modified output and envelope control circuit which may be utilized in place of a portion of the output circuit shown in Fig. lb,

as substituted for that portion of the diagram which is embraced between broken lines a-a and b-b; and

Figure 3 is a diagrammatic view of one of the playing keys and switches operated thereby.

My invention, considered generally, constitutes an improvement upon the instruments disclosed in my prior Patent No. 2,254,284, in the prior patents to Laurens Hammond Nos. 2,203,569, 2,251,- 052, 2,253,782, and in the patent to Hammond et al. No. 2,233,258.

Generating system Referring to Figure 1, the generating system is illustrated as comprising a master oscillator I0 driving a relaxation oscillator l2 of the same frequency. The relaxation oscillator I2 supplies a frequency controlling signal for a cascaded series of controlled oscillators I4, I6, and I8, which are in the form of frequency dividing relaxation oscillators, the constants of which are such as to cause them successively to halve their input controlling frequencies. This generating system may be the same as that shown in the aforesaid Patent No. 2,233,258 except that due to the fact that the oscillators may be tuned by the playing keys through the entire three octave range of the keyboard, two less stages of controlled oscillators are required.

The generating system supplies four output signals in octave relationship, the highest frequency of the soprano signal being derived from the master oscillator Ill through a conductor 20, the next highest or contralto signal being derived from the oscillator I4 through a conductor 2l, the third highest or tenor signal being derived from the oscillator I6 through a conductor 22, and the lowest or bass signal being derived from the oscillator I8 through a conductor 23, Each of the signal conductors 20, 2l, 22, 23 has a decoupling resistor RI connecting it to a manually operable coupling or register determining switch 26 by means of which the desired signals may be impressed upon the grid of a preamplier tube 28.

The master oscillator I0 is tunable through a range of three octaves plus a semi-tone by playing keys 30 designated additionally by the semitone notations of musical notes controlled thereby. Each oi the keys 30 successively operates three switches 3l, 32, and 33 in the order named. (The key 3D for the highest C note need not be provided with a switch 3|.) Condensers CI connected in series are adapted to be selectively connected by switches 3| to a grounded conductor 34 by operation of the playing keys 39, and thereby determine the resonant frequency oi the tuning circuit of the master oscillator I0. A plurality of resistor elements R2 are likewise connected in series and adapted to have their junction points connected to grounded conductor 34 by the key Y put signal, in a manner to obtain an output signal whose harmonic content diiers completely from, and to a considerable extent is independent of, the harmonic content of the input signal.

The screen of the mute tube 48 is adapted to be connected to a +300 v. terminal of the power supply by operation of a switch when the mute tube is to be utilized. To assure proper coordination between the operation of the switches 42, 52 and 18 they are preferably made in the form of three-position switches and are mechanically interconnected. In their uppermost positions, these switches permit the transmission of the signal directly from the preamplier tube 28 to the terminal 44 through the switch 42. In the intermediate positions of these switches the mute tube is effective to modify the signal, the transmission in this case being from the preamplifier tube 28 through the mute tube 48 to the terminal 44. When these switches are in their lowermost positions, the only transmission path for the signal from the preamplifier tube 28-is through the two stage odd harmonic distorter system including the tubes 46 and 48. Thus, it is possible, depending upon the positions of the switches 42, 52 and 18 to obtain an output wave shape of any one of three diierent forms, namely, (a) the output signal of the tube 28 without distortionwhen the switch 42 is closed; (b) a signal which isof the form described in detail in Laurens Hammond Patent No. 2,126,424 (particularly the description with reference to Figs. 19 and 20 there) in which the amplitudes of the harmonics tend to decrease logarithmically-with switch 42 open and switch 1D closed; and (c) the odd harmonic distortio-n by the tubes 46 and 48 previously describedwith switches 42 and 18 open and switch 52 closed.

The terminal 44 is connected to ground through the primary winding of an interstage transformer TI, which winding is shunted by selectively operable tone control meshes 12, consisting of various combinations of inductance, capacitance and resistance resonating or emphasizing different frequencies, these meshes being selectively rendered operable by opening associated tone control switches 14.

The quality 'vibrato Novel and interesting musical effects may be obtained by changing the resonant frequencies of selected meshes 12 at a vibrato or tremolo rate, such change being most effective on the resonant networks such as those illustrated for the first, second, and third voices. The means for accomplishing this result comprises a plurality of condensers Cl2, each having one terminal thereof adapted to be connected to a junction 18 through a manually operable switch 11 and a condenser CI4. The other terminals of condensers C|2 are respectively connected to switch contact arms 18 which are adapted to be periodically and sequentially connected to ground by operation of any suitable mechanism, such as a grounded cam 82 rotated at approximately '1 revolutions per second by a motor 84 through a suitable gear train. The motor 84 is connected to a suitable source of current upon closure of a switch 86 which may be closed incidental to the closure of the instruments main power supply switch (not shown);

A condenser CI3 is adapted to be connected effectively in parallel with the condensers C |'2 upon closure of a switch 88 which is mechanically connected to a switch 90, the latter switch being closed when the switch 88 is open and vice versa.

6 The switch 90 is connected in a circuit by which' the condenser CI4 may be shunted.

Assuming the switch 11 to be closed, when in the irst instance, the switches 88 and v90 are in the positions shown, that is, the switch 8B being open and the switch 90 closed, both condensers C|3 and CI4 are ineffective, and the condensers C|2, upon successive closure of the switches 18, are effectively connected Ibetween the junctions 18 and ground. When, on the other hand, the switch 88 is closed and the switch 90 open, it will be seen that the 4condenser C I 3 is in parallel with the condensers CI2 and that all of these condensers are in series with the condenser CI4 between the terminal 16 and ground. In the latter case, the effectiveness of the condensers C|2 in periodically changing the resonant frequency of any utilized networks 12 is less than when the switches 88 and 98 are in the first position. It is thus seen that the average capacity, looking into the network of condensers Cl2, CIS, and CI4 from the switch 11, is constant regardless of the positions of switches 88 and 90. This is musically desirable, and makes it easier for the player to select the tone control switches 14 necessary for obtaining a given or desired musical effect.

The over-all elect of periodically closing the switches 18 at about '7 C. P. S. is to cause the resonant frequency of either the first, second, or third voices or the resonant meshes 12 (or any combinations thereof which may be in use), to shift over a limited range, and thereby to produce a periodic tone quality change which may be perceived by the listener as a quality vibrato. The effective operation of this apparatus depends upon the fact that the input signal is a complex wave rich in harmonics. (If the signal were a simple sine wave the effect would be substantially the same as that of amplitude modulation or a tremolo effect.)

From the foregoing it will be clear that in the quality vibrato the energy in a complex signal is periodically shifted from one band of frequencies to another, although the over-all energy level is maintained relatively constant. As a result, the musical tones heard by the listener do not have pronounced or veven recognizable periodic changes in amplitude, but instead, the tones are perceived as having an indefinable richness associated with a vibrato, but, nevertheless, distinguishable from the vibrato through the fact that the tone quality instead of the pitch is varied.

Tone intensity envelope controls The transformer TI has its secondary provided with a center tap 92 and its end terminals connected to the grids 94, 95 of push-pull envelope determining tubes 96, 91. A center tap 92 on the secondary of transformer TI is connected by an attack resistor R20 to a point of fixed potential, as +43 v. An attack condenser CIG is adapted, upon closure of an attack control switch |80, to be connected between the center tap 92 and the cathodes |82, |03 of the envelope determining tubes 96 and 91. The cathodes |82, |83 are normally maintained at a potential of volts by virtue of their connection to a junction |04 of a voltage divider consisting of resistors RZI and R22. A large condenser CI1 connects the junction |84 to ground to prevent rapid transient producing changes in potential at this point. llhe junction |84 is connected through a resistor R23 with a bus bar |86 with which the key switches 32 make contact. When any of the playing keys 3G is depressed, its switch 32 connects the bus amener bar :1:09 to 4:ground :and thereby 4causes fthe potential at the junction :HM- to shift :from its `static value zof +195 wolts toa valut-:wirf` [r50 voltspthereby providing fanioperating :gridbias of -TI volts on Ythe tubes 96 and-9H,

v"lhe `attack circuit :including the .resistor 1R20, condenser 'CIiB, switch 100, voltage divider lmesh ci R21, AR22 and R23,;and.-C/If1 is ysimilar ito that shown in the aforesaid Patent No. 2,233,258 eX- cept that the aristance provided -by the resistor R23 iis, iin .said patent, lprovided by ith'e :windings of relays, and reference :may therefore be had Vto this patentv for the operation I of v:this circuit.

The .third '.key switches 533 :are adapted to connectzconductors $98 and |09 upon complete depression of fthekeys. The-conductor 10B -is -normallyiconnected -tothe screen grids M0 Vand 'I'I'I v.through va single-pole double-throw switch H2, whileth'e conductor l1091s connected fto a terminal :IISG :through la 'lowvalue anti-spark resistor'RZ. y

The terminal I-I4 fior-ms the junctionof a relatively high impedancevoltage divider mesh comprising .resistors R24 vand R251connected'between +300 mand ground. Thus, upon depression of one of the keys suiciently to operate 'its switch 33, .an v'appropriate voltage '(-l-15'0 vs) from the junction Iflll is impressed upon -the'screen grids r|10, :III to render the Itubes 96 and 91 conducting. The rate at which 'the operating yVoltage is applied to the screengrids III), III may be selectively predetermined by operating any one or more vof a=plurality of switches H8, VI I9, |29 which selectively'connect condensers-CIS, CI-9 and C29 between screens IIB, IH and ground. A resistor R21 `isconnected in parallel with the `condenser In practice, condenser 'CIS -is of relatively large value, such 'las v`1 mid., 'Cl9 is -of `lower value, such as 55 mid., and C20 is `made-off 'still lower value such as 1 mid., while R21 is `relatively high, as `1 niegohm. Thus, when anyvof the switches 33 is closed, :the rate of increase of the potential on the screens |19, III `will be vdetermined by which oz switches "H9, H9, {2i} or yfZI 'is closed,

For example, assume that `lthe switch H8 is closed. The rate at which the screen voltage is applied will then :be controlled 'by the equal value lresistances R24, R25 relative gto the capacity of Vcondenser"0118. Y It Ywill :be -noted that A.before any vof `the 'switches '-33 'is closed, the corresponding vkey .switch V32 Iwill have been closed, closure o which applies appropriate 4Opf-:rating control grid bias on tubes 95,91. Thus, when any :of the key switches .33 is closed, the screen voltage applied El therebywill causeplate current to Aflow .in .tubes T96, 91. It wlllbe apparent .that the increase v.in iplate current is controlled by the operation Yof switch-essi), and that thezrateof increase inplate .current .is determined by .the rate `at which .the screen voltage rises. If amore prompt-attack is desired switch .I [8 may 'he ,left open and switch -ILI9 closed. .In this case, both .thea-ttack and Vdecay will be .of shorter duration 4because con- .denser VCI 9 .is :smaller than condenser (1&8.

.The voltage ...divider junction IIA maybe connected'to ground through .Va relatively large condenser v.C2i uponclosurebf la switch |22.V Clo- .sure of .sw-itch |212 -causes condenser -.,C2 I to serve :as a voltage reservoirfor imparting .very prompt attack .to the-appliedescreen -yoltage when -any of the s-witchesfisiclosed. Closurejof switch 1,22, rhowever, '.cloesenot inuencethe decay rate, which :latter is entirely: affunctionof'the capacityofcon- .',densers (219,'(219. and GZlJtserving'asrrcsenvoirsof screen'voltagefaiter the depressed key is -released .sufficiently to permit its switch 33 to open. The rate :atzwhich the screen voltage decreases after all of the switches33 :are open is ldetermined b y f. le rate .at which the VScreen current discharges 'such vof thecondensers CIB, C19 and C29 as vmay have .theirassociatedswitches closed. Since the decreasefinpotentialof the screens H9, III causes .a corresponding decrease in ,plate current, the rate of vdecrease yofV screen grid potential is ynot linear, but becomes less and less rapid as the screen-voltage decreases. Thus, the vtone intensity .envelope :produced :will Vbe .similar to that Vof a @chimeinthat fthedecrease in amplitude will inirtiallybeat arelatively rapidrate and thereafter :at-progressively lower rates.

When it .is .desired to have the tones decay relatively'rapid1y,.the switches I20 and |22 are aclcsed. Under 'these circumstances the attack -will be yrapid due tothe fact that the condenser 'C21 is 'in the circuit, but the tone will likewise idecay rapidly both through the load of the tubes 96. 951 and also 'due to the load resistor R21 to .gmund As the charge on condenser C20 be- .comes :dissipated through screen current flow, 'the -eiect of R21 increases, serving further to reduce the screen potential (and resulting plate current) very-much more rapidly to cut off poftential, than if this -resistor were not in the :circuit Y .-Inorder to make it possible selectively to mainrtainthesignal transmitted by the tubes 96, 91 :atarelatively constant amplitude, there are pro- `vided a pair of resistors R28 and R29 which, .uponfclosure of switches 123 and I24 respectively, 'connect the lrelatively constant potential juncition [H4 (150 Volts) directly to the screen grids IIU and III. The resistors R28 IandR29 are of .diierent values such as 3 megohms and 1 -megohmVand arethus effective to drop the volt- .age on fthe screen grids to different values representing-final for minimum amplitudelevels of the .platecurrent of tubes96 and 91. For the values .of the circuit elements mentioned above, it is Yassumed that .the tubes 96 and 91 are remote fcutoipentodes of the 7A? type.

As previously indicated, and as will hereinafter ybe described in greater detail, the switches 33 are operated by a so-called second touch fof .the playing keys .'50, and it requires some training Yto ,acquire the proper rtechnique for playing the instrument with this second touch. .Means have :therefore been provided selectively toeliminate the-second touch feature, but never.- .theless vmaking .it possible to obtain percussion .tone intensity envelopes. The means for elimie mating the effect of the second touch switches l133 fcomprises a switch .|26 `by which the conducsters H1B .and I09 may be connected. 150i Vtith the switch |26 closed, the switch I|2 may bezswilngtoits dotted lineposition, thereby con.-

necti-ngthe screen grids IIO, I VII to the junction ITM nf .the -voltage divider through a relatively `h-igl'i resistance 'fRBD Avand connecting the screen Af5.5 agrids to ground lthrough a relatively large value :condenser C22. When these switches are thus positioned (assuming that switch |99 is open) @and no :playing .keyisdepressed the voltage on -the screen grids III), IIl is maintained at +150 .70 volts, which is thepotential of thejunction point JM. However, when fa key is depressed and the :controlgrid -bias on the tubes-96, 9.1 changed to v.rernierithese tubes conducting. kthe screen grids 1.ccmmeneeto draw current-.at'the expense ofthe y7 5 chargepn the condenser C22. The resultingdeiro creasein potential across the condenser C22 and the consequent decrease in plate current will continue until the current flow through the resistance R is sufficient to maintain the screen grids at a constant final potential. The musical effect of such setting of the switches |I2 and |26 is that the tones produced have percussive banjo-like intensity envelope characteristics.

Playing key switches In order to make it easy for the player to oontrol the intensity envelope, the key switch 33 constitutes a second touch switch which is closed only when a pressure in excess of the normal pressure is exerted upon the key. A representative construction of this type is shown in Figure 3 wherein it will be noted that the key 30 is pivoted on a fulcrum |30, and is held in position by a stud |32 passing through an enlarged opening in the end of the key stem. A compression spring |34 is provided, the degree of compression of which may -be adjusted by nuts |36 on the stud |32, which provides the force for returning the key to normal position. A suitable down stop and an up stop for the.key, of the usual construction, are provided.

The key 30 has an insulating actuating portion |38 which engages the uppermost of a series of spring fingers |40, |4|, |42, |43, |44, these switch arms being provided with suitable contacts as shown. Spring arms |40, |4| and |42 are relatively thin and flexible, while the spring arms |43 and |44 are less resilient so that upon depression of the key, the switches 3| and 32 will close in sequence, and the spring arm |43 will afford suflcient resistance to further depression of the key so that the switch 33 will thereafter be closed only when the player exerts a considerable additional pressure. It will be understood that any suitable second touch key operating system may be employed in place of that shown in Figure 3.

Volume control The plates of the tubes 96, 91 are connected to the primary of an interstage transformer T2 and are supplied with operating potential through load resistors R30 and R3l. The secondary of the interstage transformer T2 is connected to the grids |50 and |5| of volume control tubes l52, |53 which may also be of the remote cutofi` type such as the '7A7. The suppressor grids and cathodes of these tubes |52 and |53 are connected to a terminal of xed positive potential +50 v. The secondary of the transformer T2 has a center tap |54 which is connected to ground through a time constant condenser C23, and is adapted to have its potential controlled, to determine the amplitude of the signal transmitted by the pentodes |52, 53. The biasing potential is provided lby a voltage divider comprising resistors R to R49 connected to the center tap |54 through a decoupling and time constant resistor R50. The resistor R42 is adjustable so as to determine the control grid bias corresponding to maximum volume.

A volume control contactor |56 is connected to ground, and is normally in contact with all of a plurality of switch contact elements |58, and operated by a lever 51 which may be moved by the knee, foot, or hand successively to break these contacts, commencing with the lowermost contact. The lever |51 may be spring returned against a stop |59 and is moved from its full line to its dotted line position to increase the volume.

It will be noted that when the contacter |56 is in its minimum volume position, the resistor R50 is directly connected to ground so that the grids 50, i5! have a biasing voltage which is effectively 50 volts negative with respect to the cathodes. For the particular tubes used, this is near cutoff and represents the minimum volume condition. Condenser C23 and resistor render the volume increments smooth to prevent undesirably sudden changes in volume. The volume control tubes 552 and |53 have their outputs resistance-capacity coupled to a push-pull power amplifier comprising pentodes |60, IBI, the output of which is transformer coupled to a speaker |62.

It is sometimes desirable to vary the resonance frequency cf the tone control system incidental to changes in volume, to simulate the effect upon the listener of a symphony orchestra wherein as the general intensity level of the selection is decreased the tones of certain instruments seem, due partially to the room Wall reflection characteristics, to decrease in volume irregularly with respect to the change in volume of the tones of other instruments. For this purpose the volume control lever carries a grounded .contactor |63 normally (in minimum volume position) making contact with a plurality of contacts i643, and adapted successively to break the connection with the contacts 64 as the lever |51 is moved from minimum volume to full volume position. A plurality of condensers Ci2A, which correspond in function to the condensers CI2, each has one terminal connected by one of a plurality of single-pole double-throw switches |65 to the contacts |64, and have their other terminals connected to a conductor |66 which is adapted, upon closure of a switch |68, to be connected to a conductor |69 to which one terminal of each of the condensers C|2 is also connected. ,The total capacity of the condensers Cl 2A should be equivalent to the total capacity of the condensers C|2, although there may be more of vthe condensers C|2A so that there may be small incremental changes in resonant frequency as the volume control lever |51 is operated.

* The switching mechanism |53, |64 and the condensers C|2A have the effect of changing the resonant frequency of the particular tone controls in use as the volume is changed. This general effect may be accomplished by other means since the condensers C|2A or equivalent impedance elements may be connected in the output circuit in any suitable manner to change the 60 the condensers CI2A, and under these circumstances, as the volume control lever |51 is moved from minimum volume position to maximum volurne position, the quality of either the first, secf ond or third voices taken singly or in combination (depending on which of the switches 'i4 is lopen and assuming, for maximum effectiveness, that switch is closed and switch 8B is open),

.will slowly build up in sharpness of resonance 76 cuit as the volume isincreased is intended as 1-.1 representative` ofl any suitable means, such as varying the grid biasonza control tube, whereby the quality. of thetransmittedl signal, ora portion thereof, is changed irl` suitablel relationship with changes: in volume.

Modz'jed tone intensity envelope controls In some cases it maybe desirable to utilize the instrument as part'ofan orchestra ini which one player will devote his full attention to the play'- ing-'of the instrument. Since the instrument is a solo instrument that requires but one hand for the manipulation of theA playing keys, the player has the other hand free for the operation of the various controls. This. makes it feasible to rene the toneintensityenvelope controls so that more varied andY interestingv musical eifects may be obtained by the player; The means for accomplishing this result is shown' in Figure' 2 which, it will be recalled, is to be substituted for the network' between the lines a--a' and b--b of Fig: lb. In- Figure 2; the interstage transformer I-'I" has its secondary'winding connected to controlgrids H0, |12', |14, and'.|1|' |13, |15 of. parallel push-pull controltubes. |16, |18, |8'and |11, |11-9|'8| respectively, which are preferably remote cutoiT pentodes` of the rIAT type. The plates of the tubes |16 to |8| are connected in push-pull parallel' tothe primary windingL of the interstage transformer T2. The suppressor grids and cath.-

. odes of the tubes |16 to A|81l are. connected: to-

gether to the terminal' |04 of the voltage divider previously described.

The-screens of the flrst'setv of the control tubes |16, |f|1-are connectedtoaconductor |'82'through an anti-spark resistor R59' and are. connected to ground throughA an envelope' determining. condenser' C26. In a similar manner the screen grids ofpentodes |18, |19l are connected to a conductor |84, and are connected*v tov ground througha condenser C21. Likewise; the' screen grids of the pentod'es-v |80, |0| are connectedY to a conductor |86l through an anti-spark resistor R68, and areconnected" to ground through.. a Vcondenser C28, which latter isshuntedlby a resistor R52.

A switchy |88is'connectedto the conductor |08 so" asl to disconnect the. switches`33" from the circuits, and thus to renderthe' secondtouchinefifective.

There are three keys |90; |91 and'. |92 which maybe played' in conjunction'with the depression off the playing' keys- 30, therebyv to determine which ofl theV pairs Vof envelope controlling tubes n64-|11, |18|19g or M01-|81, and their associated circuits shall be determinative of the en;- velops of the tones. The keys |90, |9| and |92 are spring-returned and may, in this respect, be similar t the keys as shown in Figure 3. These keys may be operated singly or lin combination.

The envelope controlling tubes |16, |11 are proa-.sharp attack and a relatively'long decay time. The/key? |f90is adapt'edf upon depresmon to close a switch |94 which connectsthe screen grids of thetubes |16, |1-1 to a junction |0601 a Voltage divider'comprisingresistors R60 and R6| connected between al +300 v. terminal of theA power supply system and'y ground. The' resistor R64V is shunted by an attack controlling condenser C30.

Thus, upon depression of the key |90' (assuming that'- a.A signal' is supplied toI the interstager transformer TI), a screen voltageof approximately 1'501volt'swillibe supplied tothe screen grids of tubes |116, |11. This 15D volt potential` represents vided for producing an intensity'envelope havingY tio full? operating screen grid voltage*l and asl'one 'aS-"'15 12 switch |94@ i'sclosed, the plate currentsof' tubes and |1f| will be at their maximum values.'

Assuming' that one of' the' playing keysi 130 re.-

mai'ns depressed, release offkey :|90 will` result in thex relatively slow ydischarge of condenser C; which serves asa reservoir of-`screen voltage` after said key has been released. As the voltage; on condenserA ('126 decreases, thescreencur-rent also decreases. The platecurrenttheref-ore decreases and a tone intensity envelope is produced which has a smootr'r and. musically' pleasant decay rate. The` condenser. C serves 'as a screen' potential reservoir sothat when the switch` |913V is closed, the full: screen potential' will substantiallyinrmediately' be impressed upon the screens of: the tubes |16, |11, thereby causing a' percussi've or rapid'attack; The junction |86: of. the voltage' dividerv` is adapted' to be4 connected to the conductor |82 through resistors R62, R63 upon closure of switches |913. |198' respectively, these resistors be'- lng oi. different' values andservingtomaintain a potential' upon the. screen grids of.' the tubes |16', ITT for an. indefinite period aftertl'iey switch |911 has been opened,.thereby to determine. a nali'ntensity leveL-beyond which the tones-Will no. longer. decay. It Willbenot'ed'thatinelectthe switch |94. has thesarne. functionsas the second touch swtiches 3.3..

The. intensity control. tubes |18,. |10 areprovided. for obtaining alslow attack. andv avery long decay.v The conductor. |84. for` these tubesy is adapted to beconnectecl by depression of'. the key IM, and consequent closureof aswitch 200., to. a junctonpoint 202. of a-l voltagedivider compris.- ing resistors R64.- and. R65. connected between +300. v. terminal of the power. supplysystern and ground. Thus, uponclosureot the switch 200., an operating potential. of approximately 150-v volts. is impressed. upon.A theA screen gridsE ofy the tubes` |18, |19 at a rate determined,t by the condenser C22-.7 and the values of resistors R64, R65. The full operating potentialwill thereafter be maintained uponfthesel screen grids .asa long as thekey.- |91 is held: depressed; and upon'.` release ot this-key; the

potential Willidecrease ati a'veqyfslowrate, to provduce-azI` tone intensity' envelope simulating that of; a chime,.as thefcondenser C21: is discharged..

Thezenvelope control tubes.' |80; |8|f are for the purpose:Y of obtaining; aA rapidi. attack and; rapid decays, and are' underv theA control of" ther key |02 whichal when'. depressed",V successively closes switches 204i. 205%and 206. Closure of the switch 264 Vconnectsfthe conductor. |82 to; ground through a rapid; decay resistorR66Whil'e clbsureofswitch 2.05:' similarly connects". the conductor |84' to ground through a. rapidi decay resistor R61. ("llosure.Y of the switch- 266: connects the; conductor |86 to:thejunction-terminal 9.6;of the'voltage divider: comprising resistors R60 and RB l1.

The closure of thefswitches264 and 205 causes the-signal transmitted bythe tubes |16, |11; |18 andi |19 toV decay very rapidly'so that' when the switch` 2U6fis.closedf, the# signal" may rapidly build upgandiwhen the switclr206is opened; will rapidly decay to silence (and will not be transmitted by tubes |16, |11, |18 andV |19). Ifthe switches 234 and 205 wereV not' provided, this rapid decay to silence could? not occur if the player had just previously depressedkeys |96 or HTI. Such operation of key-Y |90f or key ISI would? produce a long decay envelope which might interfere with the effective operation of'thekey |921'.

Resistor R52 functions in a manner to cause rapid decay ofthe screen potential (correspond- 13 ingly the plate current of tubes |80, |8I) in a manner previously described with respect to condenser C and resistor R21 (Fig. 1b).

Operation The operation of the various portions of the instrument have been described, and it will therefore be necessary merely to summarize the operation of the instrument as a whole.

Assuming that the instrument comprises the circuits of Figs.,1, la and 1b, the musician will play it in the manner of a melody instrumentthat is, only one key at a time. In making use of the second touch feature provided by switches 33, the musician will usually play in a smooth legato manner insofar as the operation of the contact switches |3| and |32 is concerned, and Will apply additional key pressure for the operation of the switches 33 only at times when a musical accent is desired, or at other times when the percussive envelope provided by the second touch is desired. The musician will nd that by playing in a legato manner, very effective glissandos and slurs between notes may be played at low levels (that is, without the use of the second touch), whereas the termination notes of these glissandos and slurs, which are the notes actually scored, will be made relatively prominent by applying further finger pressure to operate the second touch switches and thus impart musical accents to the tones produced. This type of glissando and slur is very interesting musically because the melody notes of the musical selection being rendered stand out from the less important, but nevertheless musically pleasant, incidental, glissando, or passing notes.

Another important eifect achieved through the use of the second touch feature resides in the fact that the tones produced are devoid of any dead room effect, which would be unavoidably present in thi-s type of sustained tone melody instrument in which a single oscillator is employed. Of necessity the decay portion of the envelope associated with the switch 32 must be very rapid so as substantially to cut olf the ampliiier portion of the instrument in a time comparable to the key release time. In practice, this allowable time is very short (in the order of 20 milliseconds), and affords time sufficient only for elimination of electricaltransients such as clicks and thumps.

The second touch switches 33 and circuits controlled thereby make it possible to produce intensity envelopes having a decay period as long as two or three seconds, so that the musically desirable reverberatory effect of a large auditorium may be obtained. In addition. by making the decay rate somewhat shorter, the effect of percussion instruments may be obtained.

In practice, the playing technique is relatively easy for the musician to achieve, sin-ee he need merely use a continuous legato style with the important and accented tones being emphasized by operating the second touch switch.

When the instrument is constructed to incorporate the circuits of Fig. 2, the previously described technique of playing becomes still more versatile as the right hand is used substantially solely for determining the pitch of the tones, and the left hand is free successively to impart one or a plurality of envelopes of varying attack and decay characteristics. This makes it possible to put added vigor and life into the expression of the music being rendered a-s, for instance, by imparting sharp attack and decay envelopes on accented notes, and smooth attack and decay envelopes on notes which are played in less strict time, as in rubato passages. By having individual spring returned keys for controlling the envelopes, it is easily possible to change the character of the tone envelopes in succession in exact accordance with the change of expression desired in successive musical notes of the melody It will be noted that it is not necessary to maintain the second touch switch 33 closed throughout the time it is desired that the tone shall be sounded. The tone may be made to decay at a desired rate following the opening of the second touch switch 33. Similarly, in the embodiment shown in Fig. 2, the tone will contnue to sound at a predetermined decay rate after the envelope determining key or keys (ISU, ISI, |92) have been released. Furthermore, repetition of a single tone may be accomplished by holding the playing key depressed while repeatedly depressing one or more of the envelope determining keys.

The quality vibrato mechanism provided by the switches 'I8 and associated circuits and mechanism is of general utility and may be used with any type of musical instrument producing signals of high .harmonic development.

While I have shown and described particular embodiment-s of my invention, it will be apparent to those skilled in the art that numerous variations and alterations may be made in the circuits and apparatus without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such modications and Variations whereby substantially the result-s of my invention may be obtained by the use of substantially the same or equivalent means.

I claim:

l. In an electrical musical instrument having an electrical musical tone signal generating system and an output system including an electroacoustic translating means, the combination of a signal transmission system coupling said generating system to said output system, a pair of pentodes connected in push-pull and forming a part of -said signal transmission system, means for impressing the signals from said generating system across the grids and cathodes of said pentodes, means normally biasing the control grids of said pentodes beyond cutoff, a plurality of playing keys, means operated by said playing keys upon initial depression thereof for changing the grid bias on said pentodes to a value rendering said pentodes capable of transmitting the signal, a source of operating potential for the vscreen grids oi said pentodes, and means connecting said source to the screen grids of said pentodes upon complete depression of any of said keys.

2. The combination set forth in claim 1 in which said source is of relatively high impedance and a condenser is connected between said source and a point of fixed direct current potential to serve as a voltage reservoir at said source.

3. The combination set forth in claim 1 in which said source is of relatively high impedance, and there is provided a plurality of condensers of -different values selectively connected between the screen grids of -said pentodes and a point of xed potential to provide a gradually decreasing operating potential for the screen grids after disconnection of said source from the screen grids upon key release.

4. The combination set forth in claim 1 in which 'a plurality of resistors of different relatively high l5 value are selectively connectable between said source and the screengrids of said pentodes to maintain the screenl gr-ids at predetermined. potentials within the operating potential range thereof.

5; The combinationset forth in' claim 1 in which said sourceyis of relatively high impedance and there is provided a condenser selectively connectable between the screen gridsof sa-id pentodes and apoint of xed potential to provide a gradually decreasing operating-.potentialsource for the screen grids after' they have been disconnected from said source.

6.. The combinationv set forth in claimA 1v in which arelatively high impedance is selectively connected between said source and the screen grids to provide a pathr for maintaining an operating potential on the screen grids after'the key controlled connection between said source and screen grids has been broken by the release of the depressed key. 7.: In an electricalv musical instrument having an electrical musicaltone signal generating system andan output system including an electroacoustic translating means, the combination of a signal transmissionsystem coupling said generating system to said output system, a plurality of playing keys,- a' plurality of tone intensity envelope determining keys, a plurality of pairs of pentcd'es connected in push-pull and-forming parallelfsignal transmission paths, a sourceof screen potential, and a plurality of resistance-capacity meshes respectively connected upon operation of said envelope keys between said source and the screen' grids? of pairs of said pentodes.

8. The combination set forth in-claim 7 in which `one of said envelope keys controlstheconnection in sequence of at least two of said meshes to the screen grids of two pairs of saidV pentodes.

9. In an electrical musical instrument of the melody type having a key-controlled electrical tone frequency generating system and an output system including electroacoustic translating means, the combination of a signal transmission system coupled between the generating system and the outputsystem, said signal transmission system including a pair of multi-*electrode electron discharge devices connected in series, anda resistance mesh in the input circuit of each of said devices to limit the grid current thereof during the positive half cycle of its input signal sufficiently to cause the production of an output sig'- nal from the second of said devices in which the .even harmonics are appreciably attenuated.

' i0. In an electrical musical instrument havingf a Y- variable frequency generator and a plurality of playing keys operable to control the frequency of operation of said generator and an output system including electroacoustic translating means; the 'combination of transmission means for conducting signals from said generator to said output sys@- tem, said transmission means including a pair of electron discharge devices connected in series, each of said deviceshaving a control grid and cir- :cuit elements connected to said devices to cause lthe latter tol distort av sine wave input signal to on waveshape representing the fundamental frequency of av sine wave input' and a pronounced odd harmonic series, saidl circuit elements including current limiting resistors respectively connected in series with. said control grids;

ll. A signal transmission system for coupling the tone frequency generating system ofanielec; trical musical instrument to its output system,

the latter including. electroacoustic translating means; saidi transmission-v system comprisingVA two cathode-grid-plate electron. dischargev devicesiin series, each: of said devices comprising resistance means forming the sole connections between their respective grids and cathodes, said resistance means operating; to limit the extent ot positive swing ofthe grid by forming a path for thefilow of grid current,.and-means couplingsaid devices in series.

12. In an electrical musicalinstrumentJ the combination. of a variable frequency electrical genera-tor;l a plurality of playing: keys, three switches associated with each of said. keys a-nIl sequentially operated thereby, a signal.' transmission system, meansV controlled by the first-operated switch to determinethe frequency of operation of said` generator, means: controlled by theV secondoperated switch to condition. said transmission systemy for operation; and means; including a resistanceecapacitance meshv in said signal transmission system, controlled. by said third-operated switch to determine the amplitude cnv-elcpeofthe signaiftransmitted by said transmission system.V

13. The combination set forth in claim 12y in which-mechanical means-are provided to necessitate the operation of said. keys 4with increased pressure inorder to secure operationofsaid third.- operated switch.

14; In an electrical musical instument having a' signal generating system, an output. systemI including an electron discharge device provided with `aI cathode, control grid; anode and secondl grid, manually operable keysv forselectively controlling the transmission of musicalsignals from said generating system to the control-grid and cathode of said device, means controlled by said keys to determine the grid bias on said device,- and'additional means controlled by said: keysnear the endsof their strokes` to vary the potentialon said second grid, said last named means including a resistance and capacitance mesh Vconnected to said second grid upon the complete depression of any one of said-` keys.

l5; The' combinationset forth in claimA 14 in which said mesh-includes circuits selectivelyrenderedi eiective to; prevent the potential of said second grid' from dropping belowA a predetermined value.

16; The combination set forth inclaim`4 lli.4 in which said'meshl includes-a plurality of condensers and'selectively'operable meansfor connecting said condensersV between saidsecond gridand' a point of fixed direct current potential thereby to determine the rate-v at which the potential of said secondV grid may change from avalue at which saidl electron discharge. deviceis: renderedy coniductive tcahigher value;

la7. The combinationv setl forth in claim. is. in which. said mesh includes a condenser connected to` said second grid; and ahighresistance path for charging said condenser and maintaining said second grid ata potential atwhich said device is conductive.

18; In an electrical musical` instrument,l the combination of an electrical variable musical frequency' signal generating! system', play-ingkeys, means controlled by the partial depression of said keys for determining the pitch of the musical note frequencies-providedby said generating sys.- temi a signal transmission systemv connected to Ysaid` generati-ngsystem, said transmission system including an electron discharge -device normally non-conductive of saidI signal; means controlled bytheV partial` depressionl of said keys to. render said device conductive of said signal, a second electron discharge device in series with said iirst electron discharge device for controlling the tone intensity envelope of the signal transmitted thereby, and means operated by the complete depression of any one of said keys to change the operating potentials on said last named electron discharge device to cause the production of a tone having a percussive envelope.

19. In an electrical musical instrument having electrical signal generating means, an output system, and playing keys controlling the transmission of signals from the generating means to the output system; an electron discharge device forming part of said output system for transmitting the signal produced by the generating means, said device having a cathode, anode, control grid and a, second grid, a source of operating potential for said second grid, a resistance-capacitance network, and manually operable key means for selectively connecting said second grid to said source through a predetermined portion of said network thereby to determine the character of amplitude envelope of the signal transmitted by said device.

20. In an electrical musical instrument having electrical tone signal producing meansv and having an output system including electroacoustic translating means, a signal transmission circuit including a multi-electrode electron discharge device having a screen grid, a condenser connecting said screen grid to a terminal of ixed direct current potential, a potential source of value substantially equaling the normal operating potential of said screen grid, and e, manually operable switch for connecting said screen grid to said source.

21. The combination set forth in claim 20 in which a relatively large energy storing condenser is connected between vsaid source and a point of iixed direct current potential of value differing materially from that of said source.

22. In an electrical musical instrument having a plurality of variable frequency generators interlocked for operation at octave interval frequencies, a plurality of playing keys, means controlled by said keys for causing said generators to operate at frequencies of the notes of the lmusical scale, an output circuit for said generators, said output circuit including an electron discharge device having a cathode, control grid, anode and a second grid, means for impressing signais from said generators between said control grid and cathode, a circuit completed upon the depression of any one of said keys to change the grid bias on said electron discharge device to a value at which said device may ytransmit the signal, a third switch under each of said keys, said third switches being connected in parallel, and a resistance and capacitance network connected with said third switches -and operable to vary the `potential upon said second grid thereby to control the intensity envelope of the signal transmitted by said device.

23. Means for altering the tone quality of a musical signal to accentuate the odd harmonics thereof comprising, a rst electron discharge device having a cathode, control grid, and anode, an output circuit therefor, a second electron discharge device having a cathode, control grid, and anode, a signal input circuit for said iirst device including biasing means limiting the positive amplitude of the impressed signal to a predetermined value whereby the positive portion of the input signal wave is distorted to have a generally rectangular shape, and means coupling the output circuit of said rst device to the input of said second device including biasing means limiting the positive amplitude of the signal to cause it to have a generally rectangular shape. whereby the output signal of said second device will have a wave form representative of 'a fundamental frequency and predominant odd harmonics thereof.

24. In an electrical musical instrument having playing keys and having a signal transmission output circuit including an electron discharge device having a cathode. control grid, anode and a second grid; a resistance-capacity network cone nected between the source of potential and said second grid rendered effective upon depression of said playing keys to vary the potential on said second grid in a preselectedpotential-time pattern to cause the signal to be transmitted bysaid device to have a tone intensity envelope corresponding to said potential-time pattern, and'manually operable switches in said network for changing the potential-time pattern on said second grid which is produced when a playing key is depressed.

25. In an electrical musical instrument having an electrical musical signal generating sys.- tem. an output system including electroacoustic translating means, and a signal transmission system coupling the generating system with the output system, the combination of a plurality of manually operable keys, at least two switches sequentially operable by each of said keys when said key is fully depressed. means associated with each of said keys to impart noticeably increased resistance to depression of the key after it has operated the rst switch and prior to its operation of the second of said switches, and-means in said transmission system responsive to the operation of said switches todetermine the shape of the intensity envelope of the signal produced bysaid generating system and transmitted to said output system.

26. In an electrical musical instrument having an electrical musical signal generating system, an output system including electroacoustic translating means, and a signal transmissionsystem coupling the generating system with the output system, the combination of a manually operable key capable of movement in addition to its normal movement, two electrical control means associated with said signal transmission system and effective to determine the intensity envelope of the transmitted signal, means associated with said key for rendering said two electrical control means sequentially effective, the iirst of said electrical control means being rendered effective upon normal operation of said key, and the second of said electrical control means being rendered effective by movement of said key in addition to its normal movement.

2'7. In an electrical musical instrument having an electrical musical signal generating system, an output system including electroacoustic translating means and the signal transmission system coupling the generating system with the output system, the combination of a plurality of manually operable keys, at least two switches vsequentially operable by each of said keys, means to operate the iirst of said switches by operation of its associated key in a normal manner, means to operate the second of said switches by operation of said key to produce movement thereof lin addition to its normal movement, and means in said transmission system responsive to the ducing means to said output system, said circuit including a multi-electrode electron discharge device, aA pair of the electrodes thereof forming input electrodes connected to receive a signal from said signal producing means, another pair of the electrodes thereof forming output electrodes i connected to transmit a signal to vsaid output system, and one of the electrodes thereof being of a character such thatthe direct current potential impressed thereon determines the gain of said device, tone intensity envelope control keys, sources of relatively fixed direct current potential, a plurality of resistance-capacity meshes, and switches operated by said keys for selectively connecting said meshes between said sources and said gain controlling electrode.

29. In an electrical musical instrumentA having a plurality of playing'keys, an electrical musical tone signal generating system, an output system including electroacoustic translating means and aV signal transmission system coupling said generating system Yto said output system, the combination ofV a variable gain means in said signal transmission system, second touch means operated by the playing keysvvhen they are depressed more than a predetermined extent and including means for imparting anincreased resistance tol depression of the keys as they are moved beyond the predetermined extent, and a connection betweensaid second touch means and said variable gain means to cause the latter to effect an increase in the gain of said signal transmission circuit when` any one of said keys is depressed substantially beyond said predetermined'extent.

30. In an electrical musical instrument having a plurality of playing keys comprising a keyboard extending throughout at least' a two octave range, a master oscillator tunable throughout a frequency range equalling that of the keyboard range, a series of cascaded frequency dividing stages having their frequencies of operation stabilized by said master oscillator and each operating at a frequency one half that of the preceding stage, means controlled by operation of said keys to tune said master oscillator to a frequency corresponding to that` of a depressed key and thereby to cause said frequency dividing stages to operate at frequencies successively one octavev lower than that ofthe master oscillator, and means to selectively utilize signals from said frequency dividing stages and from said master oscillator.

3l. In an electrical musical instrument having pitch determiningl playing keys, an electrical musical signal generating system, and a signal transmission system, playing keys to control the transmission of tone signals lfrom the generating system to the transmission system, said transmission System comprising variable gain means effective to control the intensity envelope of `the transnflitted signal, and a plurality of control keys independent'of said playing keys and operable upon depression to selectively determine the rate of increase of gain of said transmission system .thereby` to determineV the rate and extent of at- Cil.

tack portion of the tone intensity envelope, and means associated with said variable gain means Iand operated upon release of the playing keyy to cause the gain to decrease at a controlled rate and thereby automatically produce the decay portion of the tone intensity envelope.

32.V In an electrical musical instrument having an electrical tone signal generating system and a signal transmission system including electroacoustic translating means, the combination of a plurality or pitch controlling playing keys, a plurality of manually operable tone amplitude control elements, means controlled by said playing keys to cause tone signals from the generating system to be supplied to the transmission system, and means in the transmission system including resistance-capacitance potential controlling circuits rendered operable by said control elements for controlling the intensity envelopes of the tone signals transmitted.

33. In an electrical musical instrument having an electrical tone signal generating system and a signal transmission system including electroacoustic translating means, the combination'oi a plurality of playing keys for determining the pitch of the tone signals supplied to the transmission system, a plurality of manually operable tone intensity envelope control elements, means controlled by said playing keys to cause tone signals from the generating system to be supplied to the transmission system, and a plurality of resistance-capacitance potential controlling circuits in the transmission system selectively rendered eiiective by said control elements to control the intensity envelopes` of the tone signals transmitted.

34. In an electrical musical instrument the combination of means for generating electrical signals representing musical tones, a signal transmission system, a plurality of playing keys operable to determine .the pitch of the tone sig'- nals supplied by said generating system to said transmission system, means including resistancecapacitance potential controlling circuits `and forming part of said transmission system for `controlling the intensity envelopes of the signals ltransmitted by said transmission system,and a plurality of manually operable keys for controlling said last named means.

35. In an electrical musical instrument having a generator capable of producing electrical sig'- nals corresponding to musical tones, a signal transmission system including electroacoustic translating means, a plurality of playing keys for determining the pitch 0f the .tone signal supplied by the generator to the transmission system, signal amplitude controlling means associated with said transmission system including a plurality of electrical resistance-capacitance potential controlling netvvorks for determining tone intensity envelopes, and a plurality of manually operable controls for selectively rendering one or more of said networks effective.

36. In an electrical musical instrument having electrical signal generating means, signal transmission means, and means for translating the electrical signals into sound; said signal transmission means comprising a plurality of electron discharge devices, each having a control grid, screen grid, cathode, and anode; means for impressing the musical signal on the control grids of -all of said devices; a plurality of playing keys; circuits controllable by said playing keys to determine the grid :bias on all of said devices; an output circuit connected to said anodes in parallel; a plurality of resistance-capacitance meshes, one associated with the screen grid of each of said devices; a source of screen grid operating potential connected to said resistance-capacitance meshes; and a plurality of selectively operable controls for coupling said resistancecapacit-ance meshes to their associated screen grids, respectively, thereby to apply operating -potentials to said screen grids at selectively predetermined rates.

37. In an electrical musical instrument which requires playing by both the players hands, the combination of a signal transmission circuit, pitch determining keys playable by one hand, tone intensity envelope determining keys playable by the players -other hand, a plurality of attack Aand decay circuits controlled by said envelope determining keys to smoothly make operative the signal transmission circuit, each of said Iattack and decay circuits including means to produce a predetermined smooth attack when its asso- REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,126,464 Hammond Aug. 9, 1938 2,161,706 Hammond June 6, 1939 2,221,188 Hammond et al. Nov. 12, 1940 2,245,354 Mroz June 10, 1941 2,254,284 Hanert Sept. 2, 1941 2,285,132 Weathers et al. June 2, 1942 2,292,757 Hathaway Aug. 11, 1942 2,294,178 Hanert Aug. 25, 1942 2,301,871

Hanert Nov. 10, 1942 

